Amendment to License Agreement

     This Amendment to License  Agreement,  dated as of ____ October 1997, is by
and among Applied Research Systems ARS Holding N.V. ("ARS"); Laboratoires Serono
S.A. ("LSA"), the successor in interest to Serono Diagnostic S.A. ("Diagnostic")
(ARS,  LSA and any  successor  thereof  being  collectively  referred  to as the
"Serono Companies") and Quantech Ltd. ("Quantech"), the successor in interest to
Spectrum Diagnostics, S.p.A. ("Spectrum").

RECITALS:

A.   The Serono  Companies  and Quantech are parties to the License,  Sublicense
     and Purchase Agreement dated November 7th, 1991, attached as Exhibit A (the
     "License Agreement").

B.   Section 2 (a) (i) of the License  Agreement  reserves from the scope of the
     license granted to Spectrum thereunder,  among other reservations,  a right
     to develop and  commercialize  the SPR  technology  for the  development of
     products to be marketed in the name of the Serono  Companies  and/or Serono
     Affiliates (the "SPR License Reservation").

C.   Section 2 (d) of the License Agreement sets forth a series of benchmarks of
     aggregate  payments  (the  "Minimum  Royalties")  and  Section  4(b) of the
     License Agreement sets forth sublicense,  assignment and transfer royalties
     (the "Transfer Royalties").

D.   Section 2 (e) of the  License  Agreement  grants the Serono  Companies  and
     Serono  Affiliates  the  right to  demand a  royalty-free  right to use any
     technology  Spectrum  has  developed  with  respect to SPR (the "Grant Back
     License"), subject to certain reservations.

E.   Upon an Event of Default, Section 10 of the License Agreement (the "Default
     Provision")  provides  that the license  rights  granted to Spectrum  shall
     terminate and revert back to the Serono Companies.

F.   The Serono  Companies  and  Quantech  wish to amend and restate the License
     Agreement  as  it  concerns  the  SPR  License  Reservation,   the  Minimum
     Royalties,  the Transfer Royalties, the Grant Back License, and the Default
     Provision.

In consideration of the agreements  contained herein and other good and valuable
consideration,  the  sufficiency  of which is hereby  acknowledged,  the parties
agree as follows:

1.   Definitions.  All of the defined terms in the License  Agreement shall have
     the same meanings in this Amendment to License Agreement.

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2.   SPR License  Reservation.  Upon Payment to the Serono Companies pursuant to
     Section  2(d) of the License  Agreement  of Minimum  Royalties  of at least
     $1,000,000 in the aggregate by December 31, 1997, the Serono Companies,  on
     behalf of themselves  and the Serono  Affiliates,  shall waive all of their
     rights under the SPR License Reservation.

3.   Minimum Royalties.  Section 2 (d) of the License Agreement shall be amended
     to read as follows:

          (d) Minimum Royalty: Notwithstanding anything stated in this Agreement
     to the contrary,  in the event that the royalty  payments  actually paid to
     the Serono Companies by Spectrum and/or any Third Party Transferee pursuant
     to Section 4 of this Agreement do not equal the following  amounts:  (a) at
     least $500,000 in the aggregate by December 31, 1993; (b) at least $850,000
     in the  aggregate  by December  31,  1995;  (c) at least  $1,000,00  in the
     aggregate by December 31, 1997; (d) at least  $1,150,00 in the aggregate by
     December 31, 1998; and (e) at least $1,300,000 in the aggregate by December
     31, 1999,  then each time one of the first three of such  benchmarks is not
     met, the cumulative  royalties to be paid to the Serono Companies  pursuant
     to Section  4(d) hereof  shall be  increased  by two  million  ($2,000,000)
     dollars so that if all three initial benchmarks are not met, the cumulative
     royalties  payable to the Serono Companies  pursuant to Section 4(d) hereof
     shall  be  increased  from  eighteen  million   ($18,000,000)   dollars  to
     twenty-four  million  ($24,000,000)  dollars.  Also if any one of the first
     three  of  such  benchmarks  is not  met  the  restrictions  on the  Serono
     Companies  pursuant to Section  2(a)(i) hereof that provide only the Serono
     Companies  and/or  Serono  Affiliates  shall be allowed to market  products
     developed   pursuant  to  the   retention  of  the  right  to  develop  and
     commercialize  SPR shall  lapse.  If  Spectrum  shall  receive any lump sum
     payment from any Third Party Transferee under a Transfer Agreement prior to
     December 31, 1999,  then Spectrum shall  accelerate  payment of the minimum
     royalties  set forth in this  Section  2(d) by paying up to twenty  percent
     (20%) of such lump sum  payment to the Serono  Companies.  It is  expressly
     understood  that such lump sum payments do not give rise to any  additional
     royalty obligations than would otherwise be payable to the Serono Companies
     under Section 4(b) and shall not increase any aggregate  minimum  royalties
     payable under this Section 2(d).

4.   Section 4(b)(B) of the License Agreement shall be restated to read as
     follows:

          (B) Commencing on July 2, 1996, each Third Party  Transferee shall pay
     Third  Party  Royalties  to  Diagnostic  equal  to the 15%  Royalties.  The
     obligation of Spectrum and any  subsequent  Third Party  Transferees to pay

<PAGE>

     Third Party  Royalties  to the Serono  Companies  shall  terminate  only in
     accordance with subparagraph 4(d) below.

5.   Grant Back License. Section 2(e) of the License Agreement shall be amended
     to read as follows:

          (e) Spectrum  Obligation to provide  technology:  Upon  termination of
     this  Agreement  under  Section  10 below,  the Serono  Companies  shall be
     entitled  to  a  royalty-free  license  to  make,  use  and  sell  whatever
     technology  Spectrum has developed with respect to SPR,  provided that such
     license  shall be  subject  to the terms and  conditions  of any  Preferred
     Transfer  Agreement  (as that term is defined in Section 6 of the Amendment
     to  License  Agreement)  which is in force  and  effect at the time of such
     termination of this Agreement.  This royalty-free  license shall not extend
     to any technology and/or data and/or patents which Spectrum  developed with
     a third  party  and with  respect  to which  the  third  party  retained  a
     proprietary right.


6.   Default  Provision.  Upon an Event of Default under the Default Provision,
     any  sublicense  granted by Quantech to a Preferred Third Party Transferee
     under a Preferred  Transfer  Agreement prior to the Event of Default shall
     survive  termination of the license and sublicense  rights in the Licensed
     SPR Technology granted to Spectrum and reversion of such license and 
     sublicense  rights to the Serono  Companies  under the Default  Provision,
     and such  Preferred  Transfer  Agreement  shall continue in full force and
     effect under  its  own  terms  and  conditions.  For  purposes  of  this  
     Section  6, a  "Preferred  Third  Party Transferee"  shall be any third 
     party  which had  assets of $100  million or more at the end of the third
     party's  fiscal year  immediately  preceding  the execution of such 
     Transfer  Agreement.  For purposes of this Section 6, a "Preferred
     Transfer  Agreement" shall be any Transfer  Agreement with a Preferred 
     Third Party Transferee which is approved by LSA, which approval will not 
     be unreasonably withheld.


7.   Execution in Counterparts.  This Amendment to License  Agreement may be
     executed in one or more counterparts,  all of which shall be considered
     one and the same agreement,  and shall become a binding  agreement when
     one or more  counterparts  have been signed by each party and delivered
     to the other party.




<PAGE>


IN WITNESS  WHEREOF,  the parties  hereto have duly executed and delivered  this
Amendment to License Agreement as of the date first above written.

APPLIED RESEARCH SYSTEMS            LABORATOIRES SERONO S.A.
 ARS HOLDING N.V.


___________________________         ___________________________

By_________________________         By_________________________

Its________________________         Its________________________




QUANTECH LTD.


___________________________

By Gregory G. Freitag
Its COO and CFO